Learning Your APCs

Architectural pervious concrete will give you a smooth, stampable finish.

From all of the articles I have read and all of the presentations I have seen on pervious concrete, one key point remains a constant: To be successful, pervious concrete must be designed with very few no fine aggregates.

But this is not always the case. There are admixtures available that allow you to add a much higher percentage of fine aggregates—sometimes as much as 100% fine aggregates—while still maintaining a healthy air void matrix to ensure adequate infiltration rates. This type of pervious concrete is becoming widely known as architectural pervious concrete (APC).

APC can give you the advantage of a smooth or stampable finish much like conventional concrete, but it still has the benefits of pervious concrete. APC can go a step further, actually performing just as natural soils do. Not only does the water run through the concrete back into the aquifer, but up to 40% will work its way back up into the atmosphere through evaporation.

These value-added admixtures definitely come at a premium cost. Some currently on the market are Percocrete (www.percocrete.com), StoneyCrete (www.Stoneycreekmaterials.com), and Ecocreto (www.ecocreto.com). Here is a close look at each.

Percocrete

Introducing Percobond admixture to a specifically designed concrete mix results in Percocrete. Percobond admixture gives the ability to design up to a 100% sand mix, along with all variations in between, while still maintaining infiltration rates of more than 200 inches of water per hour and compressive strengths from 2400 psi to 2900 psi for all sand mixes, 3200 psi to 3400 psi for 75% sand, 25% pea gravel (3/8-inch x #4) and up to 3900 psi for 50% sand 50% pea gravel mixes. Pea gravel may be substituted with a granulithic material (¼-inch x #8).

With a mix design that allows adding a high percentage of fine aggregates comes a long list of added benefits, including the ability to put a stamped finish on the pervious concrete. Until recently, stamping pervious concrete has very seldom been attempted and with little success. It has not been an acceptable method of finishing pervious concrete.

But with Percocrete, a stamped finish has a high success rate. It is also easier to introduce integral coloring into Percocrete, allowing an even dispersion of color with very little effort. A properly trained ready-mixed producer and certified applicator can gain the same smooth look as conventional concrete while enjoying the benefits of pervious concrete.

Stoney Crete

This admixture is added to the mixer truck on the jobsite. StoneyCrete gives the ability to use smaller aggregates, such as a granulithic type of material as small as 1/16-inch. It also has strengthening and self-consolidating properties, which lower labor costs as well as allow a large volume to be placed at one time.

StoneyCrete has taken pervious concrete a step further in designing and placing pervious retaining walls. This helps lower the hydraulic pressure build-up that can be detrimental to some versions. StoneyCretes strength tests are completed by running over the product with 105,000-pound dump trucks. It reportedly withstands up to 5000 passes.

Flexural strengths are 20% to 50% higher than generically designed pervious mixes. As with Percocrete, integral color is dispersed much more evenly throughout StoneyCrete than through a generic pervious mix design.